Okay, the Canon link makes sense, and it is diffractive, but the reason that it saves weight is far different from the reason that a Fresnel lens saves weight.

A Fresnel lens trades optical linearity for a reduction in mass.

The DO lens reduces weight by swapping out the second lens of a doublet (a pair of lenses that are intended to reduce chromatic aberration), which is usually a biconcave lens with a different Abbe number from its pair, for a concave-convex refractive lens that actually has a negative Abbe number.

You can see how switching from a biconcave lens to a meniscus lens gets rid of a significant amount of mass.